1. Field of the Invention
The present invention relates to an optical disc playback device that incorporates a pickup shining laser light from a light source onto an optical disc and converting light reflected from the optical disc into an electrical signal and that reads, through the pickup, information previously stored on the optical disc to achieve playback.
2. Description of Related Art
Conventionally, an optical disc playback device that reads information recorded on an optical disc such as a CD (compact disc) or a DVD (digital versatile disc) to achieve playback performs focus control for directing the focus position of emitted laser light to the recording surface of the optical disc. When this focus control is improperly performed, the information cannot be properly read from the optical disc. Thus, in order to perform the focus control properly, various devices, methods and the like are proposed.
For example, an optical disc device is disclosed in JP-A-2005-346802 that, when a difference between the address of a position from which current data is read on an optical disc and an address that a focus bias was last adjusted at and that is stored in a buffer as focus bias adjustment information exceeds a predetermined amount or when a seek is performed, determines whether the focus bias that was last adjusted deviates from an optimum value due to, for example, warpage of the optical disc and readjusts the focus bias if it deviates from the optimum value.
Disadvantageously, however, with the optical disc device described above, it is necessary to stop playback during readjustment of the focus bias. This may cause inconvenience. Since the focus bias is readjusted only when, for example, it is determined that the focus bias deviates from the optimum value, when it is not determined that the focus bias deviates from the optimum value, it is likely that focus control cannot be performed properly.
In particular, when an optical disc is eccentric, the focus position of light emitted from a light source deviates from the center position of a track formed on the optical disc every rotational period of the optical disc. Thus, it is likely that focus control cannot be performed properly.